pedagogy
27 February 2026

H2S gas: risks and challenges

Wastewater networks are essential infrastructures for our everyday lives and the preservation of the environment. However, they are sometimes the […]

Wastewater networks are essential infrastructures for our everyday lives and the preservation of the environment. However, they are sometimes the source of insidious and dangerous phenomena, such as the formation of harmful gases. One of these, hydrogen sulphide (H2S), is a serious challenge for operators and public safety. The Claire Group, which is committed to preserving water resources, has come up with innovative solutions for monitoring water networks, as well as diagnosing and controlling them, including detecting this dangerous gas. Understanding what H2S is, its dangers and how to detect it is the first step in protecting both infrastructures and people.

What is H2S gas?

Hydrogen sulphide (H2S), also known as sulphur hydride, is a gas that is naturally produced by the breakdown of organic matter in oxygen-deprived environments. It is commonly found in wastewater networks, sewers, water treatment plants, septic tanks, and agricultural environments rich in organic matter (such as manure). It is also found in certain industrial sectors (oil refining, tanneries, viscose manufacturing, rubber vulcanisation) and in natural sources such as natural gas or crude oil.

This gas is notorious for its “rotten egg” smell, detectable at concentrations as low as 0.13 ppm (parts per million = one thousandth). However, caution is advised: above 100 ppm, it causes olfactory anaesthesia, rendering its odour undetectable even at lethal levels.

With a density of 1.36 kg/m³ (compared to 1.2 kg/m³ for air), H2S is heavier than air, which means that it accumulates in low-lying and confined areas such as pipes, service tunnels and inspection chambers.

How does H2S form in sewerage systems?

In wastewater networks, H2S mainly forms as a result of the activity of sulphate-reducing bacteria. Here’s how:

The effluent, which is rich in organic matter and sulphates, arrives in an area that is low in oxygen.

Bacteria initially consume dissolved oxygen, then nitrates.

Deprived of oxygen, they then attack sulphates (found naturally in water or derived from detergents, for example) and convert them into sulphides, which combine with hydrogen to form H2S.

This phenomenon is particularly pronounced in stagnant waters, dead zones in the network, or poorly ventilated sections.

What are the hazards and risks associated with H2S?

The risks associated with hydrogen sulphide are enormous and multiple:

For human health: H2S is classified as extremely toxic by inhalation. It acts as a cellular poison by blocking a key enzyme (cytochrome oxidase), depriving cells of oxygen and directly threatening vital organs (brain, heart and kidneys).

At concentrations of 10 ppm or higher, it irritates the eyes and respiratory tract.

Between 10 and 300 ppm, it can cause headaches, dizziness, nausea, bronchitis or neurological disorders.

At 100 ppm and above, the sense of smell is lost, and the area becomes immediately dangerous to life (IDLH – Immediately Dangerous to Life or Health, according to NIOSH – National Institute for Occupational Safety and Health).

Between 300 and 700 ppm, poisoning becomes acute: pulmonary oedema, coma.

Above 700 ppm, even brief exposure can cause loss of consciousness and death within minutes.

Some chronic exposures may cause irritation, digestive or neurological symptoms.

Fire and explosion hazard: H2S is extremely flammable and can form explosive mixtures with air over a wide range (4% to 46% by volume). It may self-ignite at temperatures above 250–260 °C and react violently upon contact with oxidising agents.

Corrosion of infrastructures: When exposed to air and moisture, H2S turns into sulphuric acid, a highly corrosive agent for concrete, iron, copper and even some types of stainless steel. Result: damage to pipes, loss of seal integrity, leaks, and increased risks of pollution. This is why modern networks often prioritize plastic materials such as polyethylene (PE) or PVC, which are more resistant to this type of attack.

Environmental impact: As well as damaging networks, H2S is highly toxic to aquatic organisms. Uncontrolled discharges can disrupt local ecosystems, especially in sensitive environments.

Why is it crucial to have a better understanding of H2S?

Confronted with all these challenges (human, environmental and economic), prevention, monitoring and maintenance of networks exposed to H2S are absolute priorities. Installing rugged equipment, choosing resistant materials, monitoring sensitive areas and training teams are all essential actions for preserving our infrastructures and ensuring the safety of staff and the general public.

The Claire Group’s solutions

The Claire Group, through its Claire Connect offering, which specialises in connected instrumentation for drinking water networks, wastewater networks and natural environments, has developed specific solutions to tackle this challenge. One of these is the LOGAZ sensor, which has a central role.

This sensor has been specifically designed to measure H2S concentration in wastewater networks. It has many advantages:

Battery-operated, eliminating the need for complex connections in confined spaces.

Accurate detection and measurement of H2S concentrations, even at low levels.

Easy to use, thanks to its pre-calibrated measuring head that can easily be replaced on site.

It is versatile, as it can be used for one-off measurements as well as for ongoing monitoring campaigns, either locally or remotely.

Intelligent connectivity, with a built-in data logger that transfers data to a supervision platform, compatible with a variety of professional systems (supervisors and FTP servers). This makes it possible to monitor things remotely on a daily basis and improves the response time of teams.

How can H2S gas be detected using the Claire Group’s solutions?

As explained earlier, hydrogen sulphide (H2S) is an invisible gas, and what makes it particularly dangerous is that above a certain concentration (around 100 ppm), it becomes undetectable by smell due to olfactory anaesthesia. In other words, even though its characteristic rotten egg smell is recognisable at very low doses, it cannot be relied upon to assess the actual risk. For this reason, reliable technical detection is absolutely essential, both to ensure the safety of teams and to protect infrastructures.

What other detection methods exist?

In the professional environment, there are several methods for detecting and quantifying H2S:

Air sampling + laboratory analysis, e.g. by spectrophotometry or ion chromatography after reaction on specific filters.

Colorimetric reagent tubes, which provide a quick indication but lack the accuracy and reliability needed to compare results with occupational exposure limit values.

For effective protection, the best practice remains the installation of continuous detection systems: these devices, equipped with calibrated detectors, trigger alarms as soon as the concentration exceeds a critical threshold (e.g. 1 ppm, in accordance with NIOSH recommendations).

Lastly, it is essential to ventilate spaces properly, as H2S, which is heavier than air, tends to stagnate in low-lying and confined areas, posing an additional risk factor in the event of poor air circulation.

Why is this detection crucial?

Every year, serious and even fatal accidents are reported in connection with H2S, particularly in the wastewater treatment, water treatment, agriculture and industrial sectors (source: INRS, 2023). Therefore, having reliable tools capable of continuous detection and real-time alerts is not simply a technological convenience: it is a vital safety measure to protect operators and limit damage to equipment.

Preserving the integrity of the water network: a critical challenge

Detecting and pinpointing the presence of H2S gas is essential to achieving a fundamental objective: contributing to the sustainability of the network and guaranteeing high-quality access to water, both for today and the future. The Claire Group is committed to this responsible development approach, which aims to preserve water resources by providing solutions for monitoring and controlling water networks, from catchment to discharge into the natural environment.

The presence of H2S poses a direct threat to the physical integrity of wastewater networks due to its corrosive nature. Damage to the network due to H2S corrosion can result in leaks, ruptures and, ultimately, a loss of network performance and a risk of environmental pollution.

By detecting H2S accurately and at an early stage, Claire Group solutions can:

Protect the network infrastructure from the devastating corrosion caused by hydrogen sulphide. This represents an investment in the sustainability of the structures.

Guarantee a high-quality environment for local residents. Reducing unpleasant odours and preventing leaks directly contributes to the comfort and safety of neighbouring populations.

Quantify the effectiveness of an anti-H2S treatment (such as injecting neutralising products or injecting air to block formation) and adjust it if necessary.

Implement continuous network diagnostics, which can identify areas at risk and plan targeted actions, whether preventive or corrective.

Monitoring wastewater networks, including H2S detection, is an integral part of the solutions offered by the Claire Group for optimised management. By equipping wastewater networks with reliable, high-performance sensors such as LOGAZ, operators are empowering themselves with the means to prevent failures, secure their facilities and make a tangible contribution to preserving water resources and the well-being of the community.

The Claire Group leverages its hands-on expertise and a team of water and network specialists to support its partners in their projects, offering not only cutting-edge equipment but also the know-how to implement it optimally.